Description

Description: When NGINX Plus is configured as the data plane for NGINX Gateway Fabric, an injection vulnerability exists in the NGINX configuration generator component of NGINX Gateway Fabric. User-supplied string values from the Authentication Filter Custom Resource Definition clientID or cookieName fields, or in the clientSecret field of a Secret referenced by an Authentication Filter, are rendered directly into NGINX configuration templates without sanitization or escaping. Impact: An authenticated attacker with permission to create or modify these resources may craft values that inject arbitrary NGINX configuration directives. This is a control plane issue; there is no data plane exposure.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.1",
  "pubDate": "2026-09-02T16:17:18.663Z",
  "pubdate": "2026-09-02T16:17:18.663Z",
  "executiveSummary": "An injection vulnerability exists within the NGINX Gateway Fabric configuration generator, specifically affecting NGINX Plus deployments. The flaw resides in the improper sanitization of user-supplied input provided through the Authentication Filter Custom Resource Definition (CRD) fields, including clientID, cookieName, and the clientSecret retrieved from referenced Secrets.\nThe vulnerability allows an authenticated attacker possessing sufficient privileges to create or modify these specific CRDs to inject arbitrary NGINX configuration directives into the generated templates. This constitutes a control plane vulnerability, enabling unauthorized configuration changes that could alter the behavior of the NGINX data plane.\nWhile the impact is localized to the control plane, successful exploitation could lead to full NGINX configuration compromise. The risk is constrained to users who already maintain Kubernetes-level permissions to manipulate Authentication Filter resources. No direct data plane exposure exists outside of the side effects caused by malicious configuration injection. Organizations should prioritize access control restrictions for CRD management and monitor for anomalous configuration changes.",
  "technicalDetails": "The vulnerability is a classic injection flaw occurring during the NGINX configuration template generation process within the NGINX Gateway Fabric control plane. The component responsible for translating Kubernetes Authentication Filter CRDs into active NGINX Plus configuration directives fails to implement necessary escaping or sanitization mechanisms for specific user-defined fields.\nThe affected fields include the 'clientID' and 'cookieName' parameters directly within the Authentication Filter definition, as well as the 'clientSecret' value contained within a Kubernetes Secret resource referenced by the filter. Because these strings are rendered directly into the NGINX configuration templates, they are subject to interpreter injection.\nAn attacker who has obtained legitimate authorization to manage or create Authentication Filter resources can supply crafted input strings that break out of the intended configuration context. By injecting newline characters and NGINX directive keywords, an attacker can append arbitrary directives to the generated configuration files.\nThe attack flow follows these steps: 1) The attacker crafts a malicious payload, such as a string containing '; directive_name parameter;'. 2) The attacker inserts this payload into an 'Authentication Filter' CRD field or a referenced 'Secret'. 3) The NGINX Gateway Fabric controller processes the CRD update and invokes the vulnerable generator component. 4) The generator embeds the unescaped payload into the resulting NGINX configuration file. 5) NGINX Plus reloads the configuration, executing the injected directives. 6) The NGINX data plane adopts the attacker-controlled configuration, effectively enabling persistent control over routing, security policies, or logging behavior defined via NGINX directives.\nThis vulnerability is strictly a control plane issue, as the NGINX Gateway Fabric controller is the vector for configuration generation. The exploit requires authentication to the Kubernetes API with appropriate RBAC permissions to modify the relevant CRD resources. Once the configuration is injected, the resulting NGINX Plus process will parse and execute the malicious directives with the privileges of the NGINX worker processes, potentially leading to unauthorized redirection, information disclosure, or security bypasses within the gateway fabric."
}